A standard method for testing the shelf life of containers consist of introducing carbonated water into a set of containers and tightly capping the containers with a cap that includes a septum penetrable by a sharp needled valve. The pressure within each of the containers is periodically sampled, typically on a one-week periodic basis, with a needle type pressure gage through the cap septum. The indicated internal (gage) pressure is recorded and, using an industry standard conversion method (Zahm-Nagel, ASTM F 1115-95), the pressure is converted to volumes of CO2. One volume of CO2 is defined as the quantity of pure CO2 required to raise the internal pressure of a container by one atmosphere (14.7 psig) at standard temperature and pressure. The typical starting carbonated soft drink CO2 volume specification is 4.0 volumes where the CO2 volumes are counted starting from 1 atmosphere absolute pressure (i.e. Volumes=Atmospheres(absolute)−1).
The standard acceptable shelf life for carbonated beverages is defined in ASTM F 1115-95 as that time during which the container retains at least 85% of the original 4 volumes of CO2. Stated another way, it is the time necessary for 15% of the original 4 volumes of CO2, or 0.6 volumes of CO2, to diffuse through the container wall. Since the volume of the containers being tested does not change during the test, and the ambient temperature to which the containers are exposed is held essentially constant during the test, the 15% loss in CO2 is detected by a 15% decrease in pressure. This method is manpower intensive as container internal pressures are very sensitive to room temperature fluctuations and accuracy is often compromised due to leaks by the CO2 past cap seals and by septum penetration.
Some of the general aims of the present invention are to automate the testing, minimize temperature sensitivity, and eliminate physical measurement inaccuracies. A particular aim of the present invention is to develop an accelerated testing method to reduce testing times.
Disclosure of Invention
A testing apparatus for testing the level of retained carbon dioxide in containers according to the present invention includes engaging means for engaging an opening in said containers, the opening typically being a mouth of the container. The apparatus additionally includes gas supply means for supplying a desired quantity of a selected gas to each container, the gas typically being carbon dioxide or helium, but other gases can be used. The apparatus further includes pressure measuring means for measuring the pressure in each container, and data collection means coupled to the pressure measuring means for periodically collecting pressure data as a function of time. Ambient temperature is also measured.
The container shelf life evaluation is carried out by a series of steps including mounting a plurality of containers to the container engaging means so that they are hermetically engaged, purging any air from within the containers with a selected gas, and charging the containers to a selected volume specification with the selected gas. Thereafter the evaluation is carried out by individually isolating each of the plurality of containers, instrumenting each container with a pressure measuring means, coupling a data gathering unit to the pressure measuring means, periodically collecting data from each of the pressure measuring means, and storing the collected values thereof for analysis along with the ambient temperature values.
A testing unit according to the present invention is preferably a completely automated system where containers are purged of air with pure CO2 gas and then charged to a selected volume specification with pure CO2 gas, only achieving the same molar concentration of CO2 as with standard carbonated water methods. The containers are mounted to threaded aluminum manifolds with rubber seals to prevent leakage and each manifold station has an individual shutoff valve and pressure transducer. Once each container is mounted to its individually isolated and instrumented manifold station, a PC based computer system periodically monitors the container pressures and room temp of a custom designed multiplexer and stores the values in a spreadsheet for future analysis.
An advantage of the apparatus of the present invention is the elimination of the use of carbonated water to perform the test as it has been observed that the test results using pure CO2 gas yield nearly the same results. A further advantage of the present invention lies in the substitution of helium gas for the pure CO2 gas as the substitution allows for valid test results to be achieved much more quickly. The invention also automates the testing, minimizes temperature sensitivity, and eliminates physical measurement inaccuracies thereby arriving at more reliable results with less expenditure of manpower.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description, which when taken in conjunction with the drawings, sets forth the preferred embodiment of the present invention. The embodiment of the invention disclosed herein is the best mode contemplated by the inventors for carrying out the invention in a commercial environment, although it should be understood that various modifications can be accomplished within the parameters of the present invention.